DownloadServlet.java

package com.example;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class DownloadServlet
 */
public class DownloadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public DownloadServlet() {
		super();
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		String fileId = request.getParameter("FileId");
		System.out.println("[DEBUG] FileId=" + fileId);

		String fileName = "/tmp/" + fileId;
		String fileType = "application/pdf";
		// Find this file id in database to get file name, and file type

		// You must tell the browser the file type you are going to send
		// for example application/pdf, text/plain, text/html, image/jpg
		response.setContentType(fileType);

		// Make sure to show the download dialog
		response.setHeader("Content-disposition",
				"attachment; filename=XXX.pdf");

		// Assume file name is retrieved from database
		// For example D:\\file\\test.pdf

		File my_file = new File(fileName);

		// This should send the file to browser
		OutputStream out = response.getOutputStream();
		FileInputStream in = new FileInputStream(my_file);
		byte[] buffer = new byte[4096];
		int length;
		while ((length = in.read(buffer)) > 0) {
			out.write(buffer, 0, length);
		}
		in.close();
		out.flush();
	}
}